Back to EveryPatent.com
United States Patent |
5,061,568
|
Kessel
,   et al.
|
October 29, 1991
|
Solar screening assembly
Abstract
In a solar screening assembly optionally heatable for
defrosting/defogging/deicing which includes a plasticized polyvinyl
butyral layer and a metal/dielectric stack comprising one or more
light-reflecting metal layers and two or more antireflective layers, a cap
layer Ta.sub.2 O.sub.5 or SiOx where x.ltoreq.2, in face-adhering contact
with the plasticized polyvinyl butyral layer, such assembly when laminated
with glass exhibiting pummel adhesion of at least 3 after at least 1000
hours exposure to UV radiation in a Fadeometer, Weatherometer or
equivalent system.
Inventors:
|
Kessel; Stephen L. (Loveland, OH);
Mont; George E. (MA)
|
Assignee:
|
Monsanto Company (St. Louis, MO)
|
Appl. No.:
|
453556 |
Filed:
|
December 20, 1989 |
Current U.S. Class: |
428/437; 359/360; 359/589; 428/426; 428/432; 428/433; 428/469; 428/480; 428/699; 428/701; 428/702; 428/913 |
Intern'l Class: |
B32B 017/10 |
Field of Search: |
428/437,426,432,433,480,701,702,688,699,913,457,469
219/203
350/1.6,1.6,164
|
References Cited
U.S. Patent Documents
4368945 | Jan., 1983 | Fujimori et al. | 350/1.
|
4465736 | Aug., 1984 | Nishihara et al. | 428/332.
|
4782216 | Nov., 1988 | Woodard | 219/547.
|
4799745 | Jan., 1989 | Meyer et al. | 350/1.
|
4943140 | Jul., 1990 | Woodard et al. | 219/203.
|
4943484 | Jul., 1990 | Goodman | 428/426.
|
Foreign Patent Documents |
0263623 | Apr., 1988 | EP.
| |
WO8801230 | Feb., 1988 | WO.
| |
Primary Examiner: Cashion, Jr.; Merrell C.
Assistant Examiner: Nakarani; D. S.
Attorney, Agent or Firm: Murphy; Michael J., Farrington; William J.
Claims
We claim:
1. In a solar screening assembly which includes a plasticized polyvinyl
butyral layer and a metal/dielectric stack comprising one or more
lightreflecting metal layers and two or more anti-reflective layers, a cap
layer of Ta.sub.2 O.sub.5 or SiOx where x.ltoreq.2 in face-adhering
contact with the plasticized polyvinyl butyral layer, said assembly when
laminated with glass exhibiting pummel adhesion of at least 3 after at
least 1000 hours exposure to UV radiation in a Fadeometer or
Weatherometer.
2. The assembly of claim 1 wherein the cap layer is SiOx where x.ltoreq.2.
3. The assembly of claim 1 wherein the cap layer is Ta.sub.2 O.sub.5.
4. The assembly of claim 1, 2 or 3 wherein pummel adhesion is between 4 and
6.
5. The assembly of claim 4 wherein the cap layer is the top layer of the
metal/dielectric stack.
6. A solar screening assembly comprising:
a) a transparent substrate;
b) a plasticized polyvinyl butyral layer; and
c) a metal/dielectric stack between the substrate and the plasticized
polyvinyl butyral layer which includes one or more light-reflecting metal
layers, each surface of which is contiguous with an anti-reflecting metal
oxide layer and a cap layer of Ta.sub.2 O.sub.5 or SiOx where x.ltoreq.2
in face-adhering contact with the plasticized polyvinyl butyral layer;
said assembly in a laminate with glass exhibiting pummel adhesion of at
least 3 after 1000 hours exposure to intense UV radiation in a Fadeometer
or Weatherometer.
7. The assembly of claim 6 wherein the substrate is a glass layer.
8. The assembly of claim 6 wherein the substrate comprises a layer of
oriented polyester in contact on one side with the metal stack and on the
other side with another layer of plasticized polyvinyl butyral.
9. The assembly of claim 6, 7 or 8 wherein the cap layer comprises Ta.sub.2
O.sub.5.
10. The assembly of claim 6, 7 or 8 wherein the cap layer comprises
SiO.sub.2.
11. The assembly of claim 9 wherein pummel adhesion is between 3 and 7.
12. The assembly of claim 10 wherein pummel adhesion is between 3 and 7.
13. A solar screening assembly comprising:
a) a transparent substrate of glass or molecularly oriented polyethylene
terephthalate,
b) a metal/dielectric stack on the substrate comprising:
i) a first layer of zinc oxide on the substrate;
ii) a second layer of silver on the first zinc oxide layer;
iii) a third layer of zinc oxide on the second silver layer; and
iv) fourth layer of tantalum oxide or SiOx where x.ltoreq.2 on the third
layer of zinc oxide; and
c) a plasticized polyvinyl butyral layer in face-adhering contact with the
fourth layer of the metal/dielectric stack;
said assembly in a laminate with glass exhibiting pummel adhesion of at
least 3 after 1000 hours exposure to intense UV radiation in a Fadeometer
or Weatherometer.
14. The assembly of claim 13 wherein the fourth layer is Ta.sub.2 O.sub.5.
15. The assembly of claim 13 wherein the fourth layer is SiOx where
x.ltoreq.2.
Description
BACKGROUND OF THE INVENTION
This invention relates to a solar screening and/or electrically heatable
layered assembly employing a metal/dielectric stack and more particularly
to such an assembly which includes an energy-absorbing plastic interlayer.
Metal/dielectric stacks in window applications to reflect infrared
radiation while transmitting significant visible light are well known. The
effect is to reduce temperature buildup from solar radiation within an
area delimited by one or more of such windows. These stacks are called
interference filters and comprise at least one layer of reflective metal
sandwiched between reflection-suppressing or antireflective dielectric
layers. Likewise known is heating the metal layer by electrical
conductance to provide defrost or deice and/or defog capability.
Representative structures for motor vehicle windshields are disclosed in
International Publication No. W088/01230 and U.S. Pat. No. 4,799,745.
When such interference filters are combined with glass in laminated glazing
assemblies, particularly in vehicle windshields, it is desirable to
include a shock-dissipating interlayer of plasticized polyvinyl butyral
(PVB) in the assembly to absorb a blow, e.g. from the head of an occupant
within the vehicle, without penetrating the windshield. Various
antireflective dielectric layers as components of the interference filter
or metal/dielectric stack have been interchangably proposed for contact
with such a PVB layer as, for example, recited in U.S. Pat. No. 4,786,783.
Unfortunately, the integrity of multilayered laminated glazings which
include such interference filters and PVB layers have been less then
desirable after extended periods of use.
SUMMARY OF THE INVENTION
Now, improvements have been made in solar or heatable screening assemblies
which mitigate shortcomings of the prior art.
Accordingly, a principal object of this invention is to improve the
performance of solar screening and/or electrically heatable assemblies in
window (including windshield) applications which include a plasticized PVB
layer.
Another object is to improve the long term adhesion stability between a
metal/dielectric stack and a plasticized PVB layer during exposure to
sunlight.
A specific object is to improve the service life of solar screening
assemblies employing a plasticized PVB layer which undergo prolong
exposure to UV radiation.
Other objects of this invention will in part be obvious and will in part
appear from the following description and claims.
These and other objects are achieved in the present invention by
recognizing that certain specific dielectric layers, i.e. oxide(s) of
silicon or tantalum oxide, in contact with the plasticized PVB layer of a
solar screening assembly promote the long term stability of the bond
between the plasticized PVB layer and the solar screening assembly.
More specifically, there is provided in a solar screening assembly which
includes a plasticized polyvinyl butyral layer and a metal/dielectric
stack comprising one or more light-reflecting metal layers and two or more
antireflective layers, a cap layer of Ta.sub.2 O.sub.5 or SiOx where
x.ltoreq.2, in face-adhering contact with the plasticized polyvinyl
butyral layer, such assembly when laminated with glass exhibiting pummel
adhesion of at least 3 after at least 1000 hours exposure to UV radiation
in a Fadeometer, Weatherometer or equivalent system.
DETAILED DESCRIPTION OF THE INVENTION
This invention recognizes that i) prolonged exposure to significant UV
radiation from the solar spectrum of conventional plasticized PVB bonded
to a metal/dielectric stack of a solar screening assembly causes premature
deterioration of the bond between such two components and ii)
deterioration of such bond is unexpectedly arrested by using a cap layer
of Ta.sub.2 O.sub.5 or SiOx where x is .ltoreq.2 in contact on one side
with the plasticized PVB layer and on the other side with an
anti-reflective layer of the metal/dielectric stack. If the desired
visible light transmission and infrared reflecting levels can be achieved,
the layer of Ta.sub.2 O.sub.5 can simultaneously function as the
bond-stabilizing cap layer and the anti-reflective layer of the
metal/dielectric stack. With the silicon embodiment, a separate
antireflective layer is required since the refractive index of the silicon
compound in the stack is inadequate to provide the desired optical
properties (visible transmission and reflection and solar rejection). When
using the silicon embodiment, the value of x can vary depending on the
amount of oxidation obtained during deposition of this cap layer. This is
determined by the sputtering conditions used, e.g. deposition rate, the
power level used, the presence of 100% oxygen in the sputtering chamber of
an admixture of oxygen and another gas such as argon. The value of x or
the oxidation state for any given set of deposition conditions can be
determined by known ESCA (XPS) or AES analysis.
Stability of the bond between the plasticized PVB layer and the
anti-reflective layer of the metal/dielectric stack to long term exposure
to sunlight is measured by accelerated testing exposure of the solar
screening assembly to a source of intense UV radiation in the form of a
Fadeometer (carbon arc source), Weatherometer (xenon arc source) or
equivalent system (including a QUV system) in which a large percentage of
the light emitted is composed of UV radiation. Resistance of the bond to
deterioration as determined by the Pummel Adhesion Test further described
hereafter, is considered adequate if an assembly survives at least 1000
hours in such an accelerated exposure system. This is about equal to one
year of intense sunlight exposure as might be encountered in Arizona,
which in turn is representative of a longer period of exposure to less
severe conditions. The plasticized polyvinyl butyral layer of the solar
control assembly is well known and commercially available form Monsanto
Company as Saflex.RTM. sheet.
The metal dielectric stack component of the solar screening assembly is an
interference filter of the Fabry-Perot type designed, principally through
the appropriate selection of materials and their thicknesses to maximize
(i) transmission of visible or luminous and (ii) reflection of
heat-generating infrared portions (700-2125 nm) of the solar spectrum.
Such stacks consist of multiple, sequentially deposited planar layers of
angstroms-thick metal and dielectric coatings arranged in a predetermined
sequence in face-adhering, contiguous contact with each other, as
generally disclosed in U.S. Pat. Nos. 3,682,528 and 4,179,181.
The preferred dielectric stack contains at least two near IR reflecting
metal layers which in operative position transmit at least 70% visible
light of normal incidence measured as specified in ANSI Z26.1, this being
the minimum required in the U.S. automotive industry. Somewhat less than
this level is acceptable in less demanding architectural applications
where a single metal layer or other more light absorbing metal/dielectric
stacks may be used. Preferably visible light reflectance, normal from the
surface of the stack is less than about 8%. The metal layer(s) must be
separated (i.e. vertically in the thickness direction) from each other by
one or more dielectric layers so reflection of visible light from the
metal layer(s) interferes destructively thereby enhancing visible
transmission. Usable metals comprise silver, aluminum, chromium, zinc,
tin, nickel, brass, gold, stainless steel, copper, and alloys or claddings
of any of the foregoing. The preferred metal is silver. Metal layer
thickness should be between 60 to 200, preferably 80 to 140 A.
The dielectric layer element must be essentially transparent over the
visible range and at least one must exist between a pair of metal layers.
Preferably a dielectric layer is on each side of a metal layer. Exemplary
usable dielectric materials include WO.sub.3, In.sub.2 O.sub.3, SnO.sub.2,
ITO, Al.sub.2 O.sub.3, MgF.sub.2, ZnS,TiO.sub.2 and ZnO.
The substrate of the solar screening assembly comprises one or plural
layers, one of which directly supports the metal/dielectric stack in that
a layer of the latter rests in face-to-face contact on the substrate
surface. The substrate can be any of a variety of materials. Usable
substrates should not be prone to stretch to avoid cracking the
metal/dielectric layers and should be free of excess volatiles such as
plasticizers, water vapor or absorbed gases. The dielectric layer of the
stack in direct contact with the substrate should adhere well to the
substrate surface. Generally such dielectrics adhere well to glass,
ceramics and certain flexible plastics such as polyesters, cast acrylics,
polycarbonates, chlorinated plastics and epoxies. Uncrosslinked
polyurethanes and plasticized polyvinyl butyral as a substrate component
in direct supportive contact with the metal/dielectric stack are too soft
and extensible. Preferred substrates are sheet(s) of transparent materials
such as glass or non-extensible flexible plastic materials such as linear
polyesters, e.g. polyethylene terephthelate (PET) (or equivalent material
having the characteristics of PET) which is commercially available as
Mylar.RTM. or Hostaphan from Hoechst Celanese Corp. In a preferred
construction, the layers of the metal/dielectric stack are sequentially
magnetron sputtered on glass or a flexible sheet substrate of PET and then
the substrate carrying the metal/dielectric stack is encapsulated within
two layers of conventional plasticized polyvinyl butyral, one layer of
which abuts the PET substrate and the other of which abuts the top layer
of the stack. The multilayered sandwich containing PVB as the outer layers
is then conventionally laminated between two rigid members such as glass
panes, or alternatively may be used as a bilayer structure by laminating
it to one such rigid member intended to be the exterior side of a window.
As generally known in the art, varying the thickness and composition of a
dielectric layer spaced between the preferred two reflecting metal layer
construction, will vary the optical transmittance/ reflection properties
considerably. More specifically, varying the thickness of the spacing
dielectric layer varies the wave length associated with the reflection
suppression (or transmission enhancement) band. In addition to choice of
metal, thickness also determines its reflectivity, the thinner the layer,
the less its reflectivity. Generally, the thickness of spacing dielectric
layer(s) should be between about 200 to about 1200 and preferably between
450 to 1000 A to obtain the desired optical properties for a commercially
acceptable product. Metal oxide dielectric layers less than about 200 or
more than about 1200 A result in poor solar control properties.
Exterior dielectric layers in contact with the metal layer surfaces
opposite to the metal surfaces contacting spacing dielectric layer(s)
enhance anti-reflection performance. Exterior dielectric layers generally
should have a higher refractive index than glass or polyvinyl butyral,
i.e. greater than 1.5 and preferably greater than 1.8. The thickness of
such exterior or outside dielectric layer(s) is generally less than the
spacing dielectric layer(s) and should be about 20 to about 600 and
preferably 50 to 500 A.
The solar screening assembly of the invention can be used in any optically
transparent window application. Typical applications include aircraft,
locomotive and automotive windshields and architectural applications such
as commercial and residential buildings. By conductively associating the
metal layer(s) with a source of electrical power through the use of
conventional bus bars, defrosting or defogging or deicing capability can
be readily provided in the assembly.
The Pummel Adhesion Test was used to measure adhesion of the PVB layer to
the dielectric layer of the metal/dielectric stack with which it is in
contact. In such test, glass laminates containing the metal/ dielectric
stack and adhering plasticized PVB layer are conditioned to 0.degree. F.
(-17.degree. C.), pummeled with a 1 pound (454g) hammer to break the glass
and all broken glass unadhered to the PVB layer then removed. The amount
of glass left adhered to the interlayer is visually compared to a set of
standards of known pummel scale, the higher the number of the standard,
the more glass remaining adhered to the interlayer--i.e. at a pummel of
zero, no glass at all is left whereas at a pummel of 10, 100% of the
interlayer surface is adhered to glass. Good impact dissipation is
correlatable with a pummel adhesion value of 3 to 7, preferably 4 to 6. At
less than 3, too much glass is lost on impact whereas at more than 7
adhesion is too high and impact strength is poor.
The invention is further described with reference to the following examples
which are for illustration only and are not intended to imply any
limitation or restriction on the invention.
CONTROL EXAMPLES
Cl--Samples were prepared of standard float glass (3 in. by 4 in. by 1/8
in. thick) sputter coated with three successive layers of zinc oxide and
silver in conventional manner to provide a solar screening assembly
comprising metal/dielectric stack of the following structure and
thicknesses: Glass/ ZnO(400 A)(layer 1)/Ag(150 A) (layer 2)/ZnO(400A)
(layer 3). Thirty mil thick plasticized polyvinyl butyral sheet available
from Monsanto as Saflex.RTM. TG sheet was laminated to the exposed ZnO
layer (with an additional layer of float glass on the side of the Saflex
TG sheet not in contact with the ZnO layer) using standard laminating
conditions of 290.degree. F., 185 psi. An additional layer of float glass
was then laminated to the exposed surface of the PVB layer. The resulting
structure is representative of what would be used in a vehicle windshield.
Optical properties of the assembly after lamination to the glass were:
______________________________________
% TV % Rv % Av % Ts % Rs % As % SR
______________________________________
72.2 16.6 10.4 49.2 30.7 20.2 45.4
______________________________________
The samples were placed in a carbon arc Fadeometer with the PVB layer in
one case facing away from and in another case facing toward the carbon arc
and pummel adhesion was measured with time. For samples having the PVB
layer facing away from the carbon arc, (i.e. metal/dielectric stack facing
the arc) pummel adhesion had dropped from 3-4 before exposure to zero
overnight. For samples with the PVB layer facing the UV radiation, pummel
adhesion was zero after 3,4 days. Replacement of the zinc oxide layers
with tin oxide in another set of samples gave equivalent poor results.
C2 --An assembly of the same sputtered metal/dielectric components and
thicknesses as in Example C1 was capped by sputter deposition of about 50A
of Ti0x, where x was believed about equal to 2, on the exposed surface of
ZnO layer 3 before laminating to the PVB layer. Glass laminated samples of
this structure prepared as in C1 were tested in a xenon arc Weatherometer
with the metal/dielectric stack uppermost and facing the xenon arc. Pummel
adhesion was measured with time and results were as follows:
______________________________________
Pummel Adhesion
1000
Cap Layer 0 hrs 20 hrs 100 hrs
500 hrs
hrs
______________________________________
TiO.sub.2 on ZnO/Ag/ZnO
6 3 2 0 0
______________________________________
Control Examples C1 and C2 show rapid deterioration of the bond at the
interface between the PVB layer and an immediately subjacent metal oxide
(TiO.sub.2, SnO.sub.2 or ZnO) layer of a metal/dielectric stack. Failure
has occurred at this dielectric - PVB layer interface as opposed to the
PVB-glass interface since conventional PVB alone between glass layers will
survive indefinitely under these exposure conditions.
EXAMPLES 3 AND 4
These Examples are according to the invention.
ZnO(450)/Ag(150)/ZnO(450) metal/dielectric stacks on glass as in Example C1
were separately capped with Ta.sub.2 O.sub.5 and SiOx where x was believed
equal to 2, by magnetron sputter deposition onto the exposed surface of
ZnO layer 3 using a Leybold Heraeus sputter coater. Layer thicknesses
determined using an Inficon XTC crystal monitor were
ZnO(450A)/Ag(100A)/ZnO(400A)/ Ta.sub.2 O.sub.5 or SiOx(50A). Laminates
were prepared as in Example C1 with the exposed surface of the cap layer
in face-adhering contact with 30 mil thick Saflex TG sheet. The sequential
layers of a laminate were glass substrate/metal-dielectric
stack/cap/PVB/glass.
Optical properties after glass lamination were measured using a Perkin
Elmer 330 UV/VIS/NIR spectrophotometer with results as follows:
______________________________________
Cap % % % % % %
Example
Layer Tv Rv Av Ts Rs As % SR
______________________________________
3 Ta.sub.2 O.sub.5
70.8 17.1 11.4 47.5 30.1 22.4 46.5
______________________________________
The samples were placed in a carbon arc Fadeometer with the
metal-dielectric stack uppermost and facing the arc light source. Pummel
adhesion (average of two laminates per pummel test) measurement results
with time were as follows:
______________________________________
Example
Cap Layer 0 hrs 20 hrs
100 hrs
500 hrs
1000 hrs
______________________________________
3 Ta.sub.2 O.sub.5
9 9 8 7 7
4 SiO.sub.2 8 8 8 7 7
______________________________________
The above data dramatically shows preservation of the bond at the interface
between the PVB layer and a Ta.sub.2 O.sub.5 or SiOx cap layer after
extended 1000 hrs. exposure to intense UV radiation in a Fadeometer, as
evidenced by the pummel adhesion values of 7 for each of the samples using
Ta.sub.2 O.sub.5 and SiO.sub.2 cap layers.
Another ZnO/Ag/ZnO metal stack on float glass was capped with a 100A thick
sputter deposited layer using a different coating machine on a different
occasion from that of Example 4. Pummel adhesion of laminates containing
such a stack held constant at 9 from initial exposure at 0 hrs. through
1000 hrs. Though this value is above the desired range of 3-7 and
therefore impact absorption would be expected to be too high, the pummel
value can be easily reduced into the desired range by incorporating, in a
well known manner, a suitable adhesion control agent into the formulation
from which the PVB sheet is made. This is to be contrasted with a pummel
of <3 as in the control Examples which cannot be brought back up into the
desired 3-7 range.
The preceding description is for illustration only and is not to be taken
in a limited sense. Various modifications and alterations will be readily
suggested to persons skilled in the art. It is intended therefore that the
foregoing be considered as exemplary only and that the scope of the
invention be ascertained from the scope of the following claims.
Top